Harnessing the Power of UV (Ultra-Violet) LEDs
UV (ultra-violet) LEDs possess the remarkable ability to create captivating visual effects. Especially when their light interacts with specific colors, particularly in conditions of low ambient light. These effects are particularly pronounced when UV light is allowed to blend with reflected light in near-dark settings. To appreciate the impact of UV light, one can experiment by illuminating objects like diamonds. Which respond uniquely to this light spectrum.
Powering UV LEDs Efficiently
Most UV LEDs necessitate an operating voltage of approximately 3.6 V, corresponding to the ‘blue’ diode voltage. In this context, a MAX761 step-up switching IC is ingeniously employed to ensure a consistent current supply for biasing the UV diode. Operating in high-current mode, the IC employs PWM (Pulse Width Modulation) to regulate power delivery effectively. Moreover, it automatically transitions to PFM (Pulse Frequency Modulation) mode when operating at low or medium power levels, thereby conserving battery power. To accommodate its use with two AA cells, the MAX761 is configured in bootstrapped mode, incorporating a voltage-adjustable feedback mechanism for optimal functionality and adaptability.
Customizable Power Supply for UV LED Effects
This versatile power supply circuit allows flexibility in its power source, accommodating the use of up to four cells for operation. However, it’s important to consider the potential increase in weight when deciding on the number of cells to use, especially when crafting a portable torch light. To extend the lifespan of the switch, R1 is thoughtfully connected to the IC’s SHDN (shutdown) pin. When in shutdown mode, the circuit draws an impressively minimal current of less than 50 nA.
Decoupling for Stability
Incorporating electrolytic capacitor C1 in the circuit serves the vital purpose of decoupling the supply voltage. This decoupling is pivotal in preventing instability that can arise from the presence of undesirable ripple and noise. It plays a crucial role in ensuring the circuit operates smoothly and effectively.
Inductor Value and Type Matters
The sole inductor in this circuit, L1, offers a flexible range of values between approximately 10 and 50 μH. L1 serves as a repository for current, storing it in its magnetic field while the embedded MOSFET within the MAX761 is strategically switched. Opting for a toroid inductor in this role is advantageous as it guarantees minimal stray radiation, contributing to efficient and noise-free operation. In the realm of diodes, D1 must be a relatively fast one. The temptation to use a slower recovery diode like the 1N400x is best avoided, as it does not meet the speed requirements for this application.
Efficiency and Current Control
The circuit exhibits an efficiency rate of roughly 70%, ensuring effective power usage. The resistor R2, which is positioned on the feedback pin of the MAX761, plays a critical role in determining the amount of constant current (I) that is delivered to the UV LEDs. This relationship is expressed by the equation: R2 = 1.5 / I. The range for the current I falls between 2 mA and 35 mA, allowing for customization based on specific requirements.
Protection Mechanism with Zener Diode
The addition of Zener diode D4 offers valuable protection by acting as a voltage clamp when the load is disconnected. This safeguard helps prevent potential damage to the circuit in scenarios where one of the UV LEDs malfunctions or breaks down. In the absence of a load, the MAX761 could lead to the switching of L1 up to the boost voltage, resulting in the device’s destruction. Zener diode D4 efficiently mitigates this risk.